The present invention relates to a distributor for internal combustion engines of the electrical spark ignition type, or more in particular to a distributor having a function to suppress generation of radio noise caused by the discharge between a rotor electrode and fixed electrodes, of the distributor.
Radio noise generated by spark discharages in the ignition system of an internal combustion engine of an automobile or the like have a wide range of frequency and are likely to interfere with communication systems such as television and radio receivers over a large geographical area. Further, such radio noise is liable to give rise to a malfunction of electronic devices carried on automobiles, such as an electronically-controlled fuel injection system, an electronic anti-skid system and an electronically-controlled automatic transmission, thus often adversely affecting the running safety of the automobiles. For this reason, it is desirable to suppress the radio noise mentioned above as far as possible.
Main causes of the radio noise generated by the ignition system of an internal combustion engine include (1) a spark discharge between the electrodes of a spark plug, (2) a spark discharge between a rotor electrode and fixed electrodes of a distributor, and (3) a spark discharge attributable to the opening/closing operations of a breaker point of a distributor.
Systems which have so far been suggested for preventing the radio noise caused by the above-mentioned reason (2) may be roughly classified into (A) to (C) as follows. These systems have, however, respective shortcomings as will be mentioned below.
(A) System utilizing a resistance element inserted rotor electrode
This system is disclosed, for instance, by U.S. Pat. No. 2,790,020 patented Apr. 23, 1957 to David C. Redick et al. and assigned to General Motors Corporation.
According to this system a resistance element is embedded in the rotor electrode. The distributed capacitance formed in parallel with the resistor, however, reduces the noise suppressing effect for the high frequency range over about 200 MHz. Another disadvantage is a large ignition energy loss due to the resistance element (of about several K.OMEGA.). According to this system noise of about 5 to 6 dB may be suppressed for frequencies lower than 200 MHz.
(B) System using spraying-processed rotor
This system is disclosed, for instance, in U.S. Pat. No. 074,090 patented Feb. 14, 1978 to Minoru Hayashi et al. and assigned to Toyota Jidosha Kogyo Kabushiki Kaisha.
According to this system a high-resistance layer is coated on the surface of the rotor electrode. This system has the following disadvantages: (i) The high-resistance material layer coated on the electrode surface results in a large loss of ignition energy: (ii) Noise may be suppressed only by about 4 to 5 dB: and (iii) The coated high-resistance layer is easily detached.
(C) System with an enlarged discharge gap
This system is disclosed, for instance, in U.S. Pat. No. 542,006 patented Nov. 24, 1970 to Charles L. Dussenberry et al. and assigned to General Motors Corporation.
A discharge gap about 1.524 to 6.35 mm is formed between a rotor electrode and fixed electrodes. In spite of the superior noise suppressing effect of about 15 to 20 dB, the large discharge gap leads to a very large ignition energy loss. Especially, the recently-developed ignition apparatuses require accurate ignition with sufficient energy for dual purpose of exhaust gas purification and improved fuel cost performance. In this respect, the system (C) poses some problem.